River Crossing Puzzles

She-goat, Wolf and Cabbage

A farmer returns from the market, where he bought a she-goat, a cabbage and a wolf (what a crazy market :-). On the way home he must cross a river. His boat is small and won't fit more than one of his purchases. He cannot leave the she-goat alone with the cabbage (because the she-goat would eat it), nor he can leave the she-goat alone with the wolf (because the she-goat would be eaten).
How can the farmer get everything on the other side in this river crossing puzzle?

Take the she-goat to the other side. Go back, take cabbage, unload it on the other side where you load the she-goat, go back and unload it. Take the wolf to the other side where you unload it. Go back for the she-goat. That's it.

Cannibals and Missionaries

Three missionaries and three cannibals want to get to the other side of a river. There is a small boat, which can fit only two. To prevent a tragedy, there can never be more cannibals than missionaries together.

Family

Parents with two children - a son and a daughter - came to a wide river. There was no bridge there. The only way to get to the other side was to ask a fisherman if he could lend them his boat. However, the boat could carry only one adult or two children.
How does the family get to the other side and return the boat to the fisherman?

First go the children. Son comes back, and father goes on the other side to his daughter. Then daughter goes back to pick her brother up and they both go to the other side to the father. Son comes back to give the boat to mother who goes to the other side (to father and daughter). Daughter jumps in and goes to her brother so they can both return to their parents. Daughter gets off and son gives the boat back on the first side of the river to the fisherman, who goes on the other side. There the daughter jumps in and goes to her brother to take him back to parents where she (where the whole family meets at last) returns the boat to the fisherman.
The boat crossed the river 13 times.

Darkness Phobia

One family wants to get through a tunnel. Dad can make it in 1 minute, mama in 2 minutes, son in 4 and daughter in 5 minutes. Unfortunately, not more than two persons can go through the narrow tunnel at one time, moving at the speed of the slower one.
Can they all make it to the other side if they have a torch that lasts only 12 minutes and they are afraid of the dark?

First mom and dad - 2 minutes. Dad comes back - 3 minutes, both children go to mom - 8 minutes. Mom comes to dad - 10 minutes and they both get to their children - 12 minutes.

Frog Leap Game

Swap the frogs. 3 from the left have to jump on the 3 stones on the right and vice versa.
Each frog can jump just on the adjacent stone or jump over another frog if there is an empty stone behind it.
Click "REINICIAR" to begin.

Subtraction

Round vs. Square

Why is it better for manhole covers to be round rather than square?

You can turn a square manhole cover sideways and drop it down the diagonal of the manhole. You cannot drop a round manhole cover down the manhole. Therefore, round manhole covers are safer and more practical than square ones.

The Barbershop Puzzle

A traveler arrives in a small town and decides he wants to get a haircut. There are only two barbershops in town - one on East Street and one on West Street. The East Street barbershop is a mess, and the barber has the worst haircut the traveler has ever seen. The West Street barbershop is neat and clean, its barber's hair looks as good as a movie star's.
Which barbershop does the traveler go to for his haircut, and why?

The traveler goes to have his hair cut at the barbershop on East Street. He figures that since there are only two barbershops in town the East Street barber must have his hair cut by the West Street barber and vice versa. So if the traveler wants to look as good as the West Street barber (the one with the good haircut), he'd better go to the man who cuts the West Street barber's hair - the East Street barber.
By the way, the reason the West Street barbershop is so clean and neat is that it seldom gets customers.

Murder in the Desert

This is a story about three people (A, B a C) crossing a desert. A hated C and decided to kill him - he poisoned the water in his sack (only C had water). B also wanted to kill C (not knowing that the water of C had been already poisoned) and so B made a hole into the sack of C and the water spilt out. A few days later C died of thirst.
Who was the murderer - A or B?

Well, this is a hard one. In my opinion, there is no clear solution. Each point of view is correct, somehow. Most of the people would say that A is the murderer. Solicitor of B would stress 2 things:
1. to take away poisoned water from someone does not mean killing him,
2. B just made C live longer, even if he did not mean to (the poison might have killed C earlier).
However, solicitor of A could present the following argument:
"How can be A be punished for committing a murder by poisoning C, if C did not swallow a single drop of poison."
Raymond M. Smullyan pointed out the moral, legal and logical point of view. It is morally clear that both A and B are guilty of homicide attempt. Legally, 2 different courts could judge them in 2 different ways. And logic gives us the opportunity to write a whole book on this topic.

The Elder Twin

One day Kerry celebrated her birthday. Two days later her older twin brother, Terry, celebrated his birthday. How come?
This puzzle was submitted to Games Magazine's 'How Come' competition in 1992 by Judy Dean. It won.

At the time she went into labor, the mother of the twins was travelling by boat. The older twin, Terry, was born first early on March 1st. The boat then crossed the International Date line (or any time zone line) and Kerry, the younger twin, was born on February the 28th. In a leap year the younger twin celebrates her birthday two days before her older brother.
This puzzle was submitted to Games Magazine's 'How Come' competition in 1992 by Judy Dean. It won.